Block-based video encoding techniques are inherently lossy as they rely on quality compromises in ways that are intended to be minimally perceptible. One such compromise comes in the form of the quantization parameter (QP), which controls the degree of quantization during encoding and thus controls the degree of spatial detail retained from the original video source. As QP increases, spatial detail is increasingly aggregated, which has the effect of lowering the bit rate at the expense of an increase in distortion and loss of quality. Rate control is frequently employed in video encoding or transcoding applications in an attempt to ensure that picture data being encoded meets various constraints, such as network bandwidth limitations, storage limitations, or processing bandwidth limitations, which may dynamically change. These constraints are reflected in the target bit rate for the resulting encoded video stream, and thus the goal of rate control is to maintain the bit rate of the encoded stream within a certain range of the target bit rate, which may remain relatively constant, as found in constant bit rate (CBR) applications, or may vary as found in variable bit rate (VBR) applications. Rate control achieves this target bit rate through manipulation of QP.
The high QP typically required to achieve relatively low bit rates in conventional encoding systems often introduces quantization artifacts that are readily perceivable by a viewer. In some systems, such quantization artifacts are addressed by lowering the temporal resolution or spatial resolution of the encoded stream, which often renders the artifacts unperceivable by the viewer. However, in certain video encoding standards, such as the Advanced Video Coding (AVC) standards, a change in resolution is treated as the starting of a new video stream, which prevents the use of reference video content before the resolution change and which requires new steam information. Moreover, the downstream device receiving the encoded video stream, which often is not under the control of the same entity controlling the encoder system, may not have the ability to, or be configured to, handle the resolution change. As such, an encoding system that facilitates low bit rates and allows the original resolution to be maintained while reducing the impact of quantization artifacts would be advantageous.